Covering a truck's load bed during transportation of materials is necessary, and often required by statute, to help prevent the dangerous problem of materials being blown or jolted from the truck. Tarp extension and retraction systems for moving a tarp covering between an extended position covering a truck load bed and a retracted position leaving the cargo-area of the load bed unobstructed are standard on trucks using load beds to transport materials. The typical, prior art tarp extension and retraction systems use a manual crank system to adjust a truck bed cover between the extended covering position and the retracted loading/unloading position.
Structurally, the prior art manual crank system includes the following basic elements: a tarp reel assembly located near the forward portion of the load bed; a pair of swing arms pivotally attached to the sides of the load bed and spring biased towards the rear of the truck; a tarp with one edge attached to the tarp reel assembly and a leading edge attached to the pair of swing arms; and a crank mechanism located on one side of the truck and linked to the tarp reel assembly. While in a retracted position, the tarp is wound-up on the tarp reel assembly and the swing arms are pivotted to a forward position, leaving the cargo-area unobstructed. In contrast, while in the extended position the swing arms are pivotted rearwardly towards the truck's tailgate and the attached tarp is extended over the cargo-area of the truck.
The dynamics of the tarp system are best illustrated by describing what mechanically occurs when moving the tarp from an extended position to a retracted position. First, the manual crank mechanism is rotated causing the tarp reel assembly to rotate and wind-up the tarp. This pulls the leading edge of the tarp which is attached to the swing arms towards the front of the load bed, overcoming a rearward bias on the swing arms caused by springs attached between the sides of the load bed and the swing arms. This process continues until the cover is in a restracted position and the swing arms are in their forward position adjacent to the tarp reel assembly.
When the cover is in a retracted position the cover can be put into the extended position by releasing the lock on the crank mechanism. The spring bias then pulls the swing arms towards the truck's rear and the attached tarp is pulled over the load bed.
In order to operate the cover mechanism described above, four main steps are required of the operator. First, the operator must get out of the truck and go to where the crank mechanism is located on the truck. Second, the operator must remove the crank mechanism from its locked position. Third, the operator must mannually control the rotation of the crank. Last, the operator must place the crank in a locked position.
The safety of the operator, the number and difficulty of operator steps, and durability are all factors in determining the effectiveness of a tarp system. An examination of each of these factors with respect to the above described prior art cover system reveals many problems in the prior art design.
First, the cover system is not operator safe because of the substantial rearward spring tension on the swing arms when the tarp is in a retracted position. Tension in the swing arms results in a substantial corresponding rotational force in the crank mechanism at high velocity. Thus, a dangerous situation is created such that the operator must grip the crank firmly and continuously when manually rotating the crank to prevent the counter-rotational force from causing the crank to forcefully rotate out of control. If the crank slips from the hand of the operator, which is not unlikely due to the considerable rotational force on the crank handle, or if the operator inadvertently releases the handle before locking the crank, the crank may forcefully rotate out of control and strike the operator standing nearby.
The operator steps required to adjust the tarp also unnecessarily complicated, time consuming, and inconvenient. As previously described, the prior art tarp system requires the operator to leave the truck's cab and perform a series of manual steps to alter the position of the cover. A tarp system permitting the operator to alter the position of the tarp in a simpler, more convenient manner is desired.
Prior art tarp systems also fails to recognize or account for an important problem which may result from operatorerror. Conventional dump trucks include a hydraulic dump cylinder for moving the load bed from a horizontal to a vertical position to dump material from the load bed. For the dumping of most materials, the tarp should be in the retracted position to ensure that the cover will not be in the path of the flow of material during unloading. The prior art tarp system provides no safety feature to help prevent the operator from inadvertently raising the load bed to unload the material without placing the tarp in a retracted position. Hence, through operator error the cover may be in an extended position during unloading resulting in the cover being in the path of the material flowing from the truck bed. This scenario may result in substantial and expensive damage to the cover mechanism.
Last, the external positioning of the prior art cover mechanism may result in problems and reduce the overall durability of a truck. For example, trucks used to transport loose materials often must be closely maneuvered around various obstructions and structures in order to load or unload material. During this maneuvering, a tarp system mounted on the side of a truck is exposed to damage caused by the truck grazing or striking obstructions located along the truck's path. The crank mechanism of the prior art tarp system has the problem of being exposed on the side of the truck reducing the durability of the tarp system.
There is a distinct need for a cover mechanism which reduces the risk of danger to the operator, reduces the number and difficulty of operator steps, provides safety features to help prevent operator error, and increases the durability of the cover mechanism.